Yep,  I recently sorted through a bag of 100 crystals from China ($10, shipped) looking for a "good" one.  They were ALL good...  a complete waste of time.  I was rather amazed at their consistency and performance for a 10 cent part.

Last year I bought an alarm clock / game from China (looks like 7 sticks of dynamite with an ominous circuit board / LED display strapped to it).  It uses a 40 pin (AVR?) processor driven by a 16 MHz processor crystal.  I have not set it in over a year and it is still within a few seconds.  I suspect they measure the frequency and have a calibration tweak stored in EEPROM... but that seems excessive work for a $20 toy.  I highly doubt they go as far as doing temperature compensation.  Maybe they characterized a bucket of XTALs and use a generic compensation factor?

It’s likely that your whole bag of 5,000 came from the same bar and your
net result will all look a lot alike…..

Hi

You could calibrate the nominal frequency a chip very cheaply these days. They may / the
may not, who knows. It certainly is done that way on very low cost wrist watches.
I’d bet that they do and it leaves the factory set within less than 1 ppm.

A good generic crystal is still going to be a few ppm sort of proposition once set. Each ppm is 2.6
seconds a month. If you only get bothered by it being off one minute, it’s quite possible
for a simple clock to hang in there for a year.

The interesting thing is that most places set the device to run fast. There are some
great sites on the internet documenting this. You normally are bothered by the
deliberate offset before you notice the actual accuracy of the clock.

Bob

I've been very impressed by the LED/VFD car clocks that come built into
cars for the past 20 years. They have to work in temperature extremes from
below zero to way above 120F when parked in the sun on a hot day. And every
six months at DST time when it's time to reset them, I find they are never
off more than a minute. This leads me to believe, they must have some sort
of temperature compensation (I'm guessing a lookup table or maybe just a
simple few-parameter formula to adjust divide-down clock based on cheap
temperature sensor) built in.

Tim N3QE

On Sat, Oct 22, 2016 at 10:52 PM, Mark Sims holrum@hotmail.com wrote: